This sporting monthly, which began publication in 1831, is not to be confused with the older Sporting Magazine, which began publication in 1793.
The February, 1838, issue included an article on "Historical Notices of the Dog," which examines dog-related art and statuary going back to biblical and ancient Egyptian and Greek eras. Its only mention of Newfoundlands follows:
One of the finest specimens of ancient sculpture which has come down to modern times, is the figure of a dog, generally called the dog of Alcibiades, and supposed to be the production of
Myron, a statuary famed among the ancients for his admirable representations of animals. . . . Some writers have described the figure as that of a mastiff, but it certainly bears little resemblance to the dog known in England by that name, being much more like the Newfoundland dog, though not so shaggy nor so thick and short in the neck. (100)
That statue (also known as "the Jennings Dog" after an early owner) is of a dog now identified as a "molossor," which as an ancestor of the mastiff would indeed be a (remote) forefather of the Newfoundland. Read more about, and see an image of this statue at Wikipedia.
Alcibiades was a 5th Century BCE statesman, general, and orator in Athens; he famously owned a large dog with a docked tail, and because the tail of this statue is broken off, his name became associated with the statue although it has no real connection to either Alcibiades or his actual dog.
The "dog of Alcibiades" is also mentioned, and linked to the Newfoundland, in William Youatt's 1845 book The Dog, as well as in Estelle Ross' 1922 work The Book of Noble Dogs, both of which are treated here at The Cultured Newf.